The authors present an overview of possible mechanisms for cardiac stimulation. Changes of the transmembrane potential in the myocardium in response to an applied electric field are produced by two types of mechanisms, continuous or discrete, depending on whether they are associated with complete or incomplete current redistribution between the intracellular and extracellular spaces. Another way of classifying these mechanisms is whether they produce a membrane polarization only at the heart surface, or both at the surface and throughout the bulk of the heart. These categories provide a unifying framework for future studies on the mechanisms of field stimulation of the heart